Lord Neuberger, the president of the UK’s supreme court.
Photograph: Luke Macgregor/Reuters

In a BBC interview this week, the president of the United Kingdom supreme court posed an apparently simple question. After Brexit, Lord Neuberger asked, should the UK judges take into account the rulings of the European court of justice or not? Britain’s most senior judge, who steps down next month, was very clear about his own answer: “If the UK parliament says we should take into account decisions of the ECJ then we will do so. If it says we shouldn’t then we won’t.”

Constitutionally, this was an impeccable answer to his own question. Parliament makes laws; judges interpret them. Yet politically, and even legally, it leaves many profound questions unresolved. The starting point of Lord Neuberger’s unease may well be the current drafting of clause 6 of the government’s EU withdrawal bill, which says that the UK court “need not have regard” to the ECJ’s rulings after Brexit day, while adding that it “may do so if it considers it appropriate to do so”. In essence, this means the decision to take account of the ECJ is up to the UK courts.

As guidance to the judges, that formulation is neither as daft or as buck-passing as it may look. In reality the draft clause reflects current judicial practice in the UK, which for years has been to take account of rulings in other jurisdictions (like the United States, Canada and elsewhere) where that is appropriate, though without being bound to do so. In that respect, the bill merely adds the ECJ to the list of courts that the UK judges can take account of if they choose.

But that is where serious politics kicks in. Theresa May regards ending the role of the ECJ as a major prize of Brexit. It is one of her red lines. Conservative anti-Europeans have made the break with the ECJ into a totem of their yearned-for independence from all things European. The political logic of the government’s position is therefore different from the permissiveness of its own draft clause. It is that Britain’s judges must act as if the European court simply does not exist.

This would have huge legal, as well as political, implications. Comparative international law and national law are deeply entwined. As the late Lord Bingham pointed out in his book The Rule of Law, UK courts already have to take account of international law and precedent in issues as diverse as aviation law, commercial and intellectual property law, crime, employment, industrial relations, the environment, treaty obligations, family law, human rights, immigration, immunities, the law of the sea and the laws of war and weaponry. Countless leading judgments in UK law routinely reflect this reality. Courts in one country learn from courts in another. In the phrase of the former president of the Israeli supreme court, Aharon Barak, comparative law is “an experienced friend”.

To exclude the UK courts from considering European rulings would therefore punch a large, arbitrary and utterly perverse hole in a system of comparative law that has been of historic benefit to international fairness and decency in many lands. It would mean that the UK courts could cite rulings by the US, Canadian and many other courts, but not those of our European allies and neighbours, with whose laws ours have been intimately entwined for nearly half a century. Reactionary judges – like the late US supreme court justice Antonin Scalia – hate such cross-fertilisation. Enlightened judges welcome it, and are right to do so.

Lord Neuberger nevertheless seems to fear a trap. The anti-European press’s “enemies of the people” onslaught, and the scandalous failure of ministers to defend judicial independence, cut very deep. Lord Neuberger surely does not want the judges to risk another populist fusillade whenever they uphold “Europe” after Brexit, as the bill would permit them to do. That is why, though apparently simple, his question matters.

It is also why ministers should come clean. The draft clause in the EU withdrawal bill may not be perfect, but it is far preferable to any attempt to proscribe the ECJ from UK judicial thinking. The consequences of preferring it are profound and desirable. The ECJ should continue to have a proper, though inevitably different, role in UK law after Brexit. The exceptionalist red line must be erased. Mrs May should explicitly permit the UK courts to take account of ECJ rulings.